My 2005 Honda Civic is losing electrical power periodically. Most noticeable is the radio turning off then immediately back on. It has now started to show various start up lights. Sometimes the ABS, parking break, or other lights, sometimes all, sometimes one but always the radio will go out. There's a slight 'shutter' when it happens from the engine, then all is okay. It doesn't happen at any particular time. I can be stopped, or driving, smooth roads or bumpy.

I don't think your radio has anything to do with them not working, check you fuses.

there are 3 power sources to radio. if stock, if not stock more.
Radio power.
memory power
and dial lamp power. (dimmer)

why not use a voltmeter to find out why its dead.
even better the FSM shows the wires, the colors and the path.
making guessing go to zero.

when working electrics pull battery minus lug, like the FSM directs you.
and keys in pocket. causing load dumps can cause very expensive
electronics to fail. even the EFI, PCM.

It sounds like you have a major electrical issue or bad (shorting) battery. When you say it loses all power, you mean radio, lights, horn etc? Clean Battery terminals & look for ground wires that need to be cleaned & reattached. Check the black ground cable that goes to engine block. The more I type the more I think its a bad ground somewhere or the battery is shorting out inside the case. Good luck and I hope this helps you.

you may have a faulty alternator or and internal part in the alternator, replace it with a dealer part and that may solve the problem, it must be a dealer part..

Check the main fuses under the hood. There are several large ones there. A loose connection on one of them could have caused the sudden, complete electrical failure you described. If it is a loose connection, it would certainly explain why it "came back to life" by itself.

Also, might you possibly have any sort of aftermarket security system that has an immobilizer feature on it? While I wouldn't expect this to disable the entire car including the radio, if it were incorrectly installed I suppose it could.

I hope this help. Good luck!

see if you can duplicate the problem with the car sitting still, key in the on position. gently wiggle the key to see if the problem occurs.

The alternator is dying...
It is not charging your battery. Don't use your headlights (big power drain) until you have the electrical checked.
AutoZone will analyze (free) w/o removing alternator (IN-CAR test)

Hope this helps, soon!

Just turn the acc switch on, turn on the radio and press the code numbers using the numbers on the radio faceplate.

U will need to replace the ignition switch, this is not the key cylinder but the actual electrical switch the key cylinder operated. see photo. I noted that on your model Honda the switch comes with a new key cylinder, you can just use the switch and use your old cylinder over or install the new parts together.